The present invention relates generally to firearms employing rifled gun barrels, and particularly to gun barrels in which gain twist rifling is desired.
The provision of gain twist rifling in gun barrels is well known and comprises the alteration of the rifling grooves in pitch at least once along the barrel length, to either, for example, increase or decrease the axial distance between respective grooves.
The prior art techniques for providing gain twist rifling comprised the employment of a series of cutter devices, each defining a progressive increase in the cutting diameter, to gradually cut out the full extent of the rifling grooves. The cutters conventionally defined an essentially circular circumference along which were regularly placed a plurality of cutter elements that were adapted to enter and increase the depth of the rifling groove initially inscribed within the barrel.
The employment of stationary cutters in a regular sequence was conducted by separate operations, wherein each cutter was sequentially passed through the length of the gun barrel. This procedure was extremely time and energy consumptive. Attempts to shorten the procedure by seeking to make cuts of greater incremental diameter were unsatisfactory, as greater resistance offered by the additional metal sought to be removed, required an undesirable increase in the power needed to drive the cutters and also adversely increased tool wear, thereby decreasing tool life.